This is absolutely amazing!! Previously on this forum we spent about
a month and 1000 messages on this topic. Now, one message gets generated
about the Johnson match box and its going full bore again.
I enjoy antennas and the like but I really don't think this is the place to
go
over the merrits of the 1950 era johnson match box. I think my 1950 ARRL
handbook is the place for this.
Carl Moreschi N4PY
----- Original Message -----
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@ames.net>
To: "Sherrill WATKINS" <SEWATKINS@dgs.state.va.us>
Cc: <tentec@contesting.com>
Sent: Thursday, April 05, 2001 2:06 PM
Subject: Re: [TenTec] Johnson Antenna Tuners article in Electric Radio,
March 2001.
>
> I've used various feed lines, one of the earliest was telephone company
> direct burial cable that had a spiral wrapped strip of phosphor bronze
> for a mechanical and electrical shield. It was destroyed by lightning
> that hit the corn crib holding up the SW end of the wire. I know I tried
> TV twinlead, but found that it had too effective an air foil and the
> small ratio of copper to surface caused it to break from flapping in the
> winds far too often. Then I went to 3/4" spaced #18 copperweld (a
> commercial feed line) which tended to last longer so long as there was
> no ice. Any breeze at all with it or the twinlead covered with ice broke
> the feed line into short lengths. The last feed line had several splices
> as the result of such ice. I was tempted to make a feed line of #10
> copperweld spaced a couple inches, and have the materials but never got
> around to doing it. The double extended zepp and feed line are wadded
> and tangled in a tall grass patch out back. I need to dig them out for
> future use.
>
> I probably had some feed line radiation at 6m and 2m. My first batch of
> 3/4" spaced line came from W0PFP who found it lossy on 6m due to
> radiation when he turned corners with it. My run was stretched straight.
> I tied a piece of about 3/16" nylon to half a dozen spreaders (clove
> hitch about each) at each end and tied that nylon to the center
> insulator at the top and to a concrete block on the ground and raised
> the center with a halyard over a pulley until the line was tight.
>
> Back in about 1964, I was experimenting with a monimatch type III or IV
> (wire pulled under the braid of a coax) SWR meter. I noticed that for
> shorted coaxes that I could detect a change in SWR that seemed to
> correspond to the published line loss (at 2m). So to check some K-200, I
> built a coaxial balun. Checked it with a short across its terminals and
> had about enough added loss to account for the expected balun loss. Then
> I hooked in a few feet of K-200 with its conductors bent over and
> soldered to make a good DC short. SWR was 1:1... There was no reflection
> from that short... Which made it seem as if the RF was just using the
> dielectric as a guide (e.g. a 2 wire Goubot line). When I moved a sheet
> of copper a couple feet on a side up to the short at the end of the
> K-200, I then developed the SWR that I expected for the line loss of the
> K-200 and the rest of the test setup. That experiment showed me that the
> conductors and dielectric of the balanced unshielded line seemed to be
> mere guides for a traveling field, not containers.
>
> K-200 was about 3/4" spacing, about #12 conductors in a big oval of
> polyethylene. Very HEAVY DUTY.
>
> There have been many sizes of TV twinlead. The best aren't in the
> discount stores where the lead is often miniature, under 3/8" wide with
> #24 conductors. The better TV twinleads of the past were more like 5/8"
> spaced #18 or 20 in considerable dielectric, UHF twinleads tended to
> have a hollow oval of dielectric.
>
> Some EME operators, especially in Europe, believe that using a multi
> yagi phasing harness of open wire lines (all straight) results in better
> array efficiency than using low loss coax in the feed harness at least
> up through 432 MHz. And they test it by working with signals at
> threshold where a half dB difference in antenna loss can mean 3 or 4 dB
> difference in signal to noise. Their lines tend to be about 1/2" spaced
> (with teflon spacers) #12 copper.
>
> 73, Jerry, K0CQ
>
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